How to Choose Between Fine Pole Magnets and Hard Milling Magnets

When comparing Fine Pole Magnets to Hard Milling Magnets in work-holding applications, it is important to consider these three key factors:

Specific application / manufacturing environment

Performance

Cost

Let’s look into how these two magnetic solutions compare.

Fine Pole Magnet (FPH*)

Manufacturing environment

The FPH magnetic circuit is designed specifically for the sinker electrical discharge machining (EDM) environment. It is also used in the grinding environment as it meets the performance requirements there.

Performance

The FPH allows for the EDM process to continue into the surface of the magnet if necessary without any re-burn due to materials staying in suspension. This is an area where the strongest magnet is not the “best” magnet.

Hard Milling Magnet (HSM*)

Manufacturing environment

The HSM magnet is designed specifically for the hard milling area. It has the highest strength of any permanent magnetic circuit. The HSM magnet generates a primary and secondary field which allows it to provide a strong holding force while not magnetically penetrating deep into the part, hence minimizing chip contamination in the cutting zone.

Performance

While this circuit does not penetrate deep, it does create a situation where use in the sinker edm should be avoided. If an electrode tip is within approximately .25” of the magnetic surface and you are in a situation where the length /depth ratio of the area is greater than 5, you can get reburn. As the electrode cycles the coolant is evacuated from the hole and some solids can stay in magnetic suspension. When the electrode returns to the hole, we can get depth & finish problems.

Note that while we recommend the FPH magnetic circuit for sinker EDM for the reason described above, Hermann Schmidt does have customers that successfully use HSM magnets just fine in the EDM environment.

Comparing Cost

The HSM magnets cost 30% more to build and it is reflected in the price. Many customers want just one type of magnet to do all the work. We believe that is usually not reasonable. At Hermann Schmidt, we build magnets for the manufacturing environment and do not recommend trying to make a magnet design work where it does not belong.

Choose the Right Magnetic Tools for the Environment

Between selecting between fine pole magnets and hard milling magnets, consider the manufacturing process and the performance requirements first. Once that is established, the cost can be factored in – with cost going well beyond the initial purchase price.

* Throughout this post we used our FPH and HSM abbreviations to match our corresponding product lines. When selecting the correct magnetic tool for your specific application from Hermann Schmidt, look for models with the matching designation. If you have any questions about using the right tool for your application, please give us a call at 860.289.3347.